In recent years, a light emitting diode (LED) using a light guide panel and an organic light emitting diode (OLED, hereafter, it is also called as an organic electroluminescent element) have been attracted attentions as a flat panel light source. An LED with a light guide panel (hereafter, it is called as a light guide panel LED) has been used not only for a general illumination, but for various situations and purposes such as a backlight for a liquid crystal display (LCD) (for example, refer to Patent Document 1).
In particular, it has been rapidly increased the use of smart devices such as smart phones and tablets. In many cases, the smart device is provided with buttons of fixed functions and fixed shapes (hereafter, they are called as “common function key buttons”) such as: a “home” button indicated by a square mark; a “return” button indicated by an arrow mark; and a “search” button indicated by a magnifier mark, in the outside of the main display.
These common function key buttons have a composition as follows. Generally, a deflection pattern of a dot form is printed beforehand on a light guide panel according to a pattern form of a mark to be displayed. Then, there is placed an LED light source to irradiate light to a side-edge surface of the light guide panel at a side surface of the light guide panel. With respect to the common function key button, the emitted light from the LED light source enters the side surface of the light guide panel, and the incident light is totally reflexed to the front surface direction of the light guide panel through the deflect reflection surface of the deflection pattern. By this, the light is taken out from the front surface side of the light guide panel, whereby it becomes possible to see the emitted pattern when viewed from the front surface of the light guide panel.
A generally used smart device contains a standard function of changing a direction of the main display according to the direction of the smart device. For example, when the smart device is rotated clockwise by 90°, the indication of the main display is also rotated clockwise by 90°.
However, the above-described common function key button cannot be changed with the direction of the mark or any required form at the same location in accordance with the direction of the smart device.
A generally used common function key button usually adopts a light guide panel LED as describe above. The common function key button having this constitution has the following features.
For example, in order to change a direction of a mark or any required optional mark, it is required to laminate a plurality of light guide panel LEDs. However, the laminated plural light guide panel LEDs have an increased thickness and they cannot be incorporated in an inner portion of a smart device.
In addition, in a common function key button adopting a light guide panel LED, light is introduced from the side-edge surface of the light guide panel. As a result, emission unevenness becomes remarkable depending on the design and the shape of the common function key button.
Further, since the mark of the common function key button is formed with a deflecting material having a dot shape and printed on the light guide panel LED, the deflecting material of dot shape is also visible, and it cannot clearly display the light emitting pattern.
However, when a common function key button is displayed by using an organic EL element containing a plurality of laminated light emitting units in which a different light emitting pattern is formed (patterned) in each unit, the above-described features will not be produced. Namely, by changing the light emitting unit to be lighted in accordance with the direction of the smart device, it is possible to change the light emitting pattern of the organic EL element. Further, since the organic EL element as described above is very thin and flat, it can be incorporated in the inner portion of the smart device.
As a method of patterning the light emitting unit, Patent Document 2 discloses a method of modifying the light emitting function of the irradiated portion by irradiating with UV rays.
However, Patent Document 2 does not disclose a method of patterning different patterns to a plurality of light emitting units.
In addition, it is conceivable to form an organic functional layer having a different light emitting pattern in each light emitting unit with film formation using a mask. However, there will remain a feature of low shape accuracy of the light emitting pattern only by using a method of patterning to form an organic functional layer with a mask.